Fun Science Idea

The weight of an automobile can be determined using little more than a tire pressure gauge and a ruler.

The area of a tire that is in contact with the ground is very close to being a rectangle. First the length and width of that area are measured. The two measurements in inches are multiplied to give the square inches of area(since the area of a rectangle is its length times its width). The force in pounds on each square inch is the pressure inside the tire as measured by the tire pressure gauge. The total weight on that tire is the number of square inches times the pressure on each square inch.

Park the car on a smooth flat surface such as concrete or blacktop. From the rearward direction, slide a rectangular piece of cardboard under the tire as far as it will go. Slide a second piece under from the front. Measure the distance between the two pieces. Then slide a piece in from each side and measure the distance between them. Those distances are the length and width of the area that the tire pushes on the pavement.

The two distance measurements should be in inches if the tire pressure gauge gives readings in pounds per square inch. Multiplying the two distances together would give the area in square inches. The weight in pounds then is the product of the area and the pressure.

weight(pounds)=area (inches times inches) times pressure (pounds/[inches times inches])

Since there are four tires the total weight  of the car would be about four times the weight that we calculated. A car is usually designed with about 60 percent of its weight on its front wheels and 40 percent on the rear wheels. But that varies. So to get a more accurate figure, use the above method to calculate the weight on a front tire and a rear tire. Add the two numbers and multiply by two.

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